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  <section id="debug-messages">
<span id="library-debug-messages"></span><h1><code class="docutils literal notranslate"><span class="pre">debug_messages</span></code><a class="headerlink" href="#debug-messages" title="Link to this heading"></a></h1>
<p>By default, <code class="docutils literal notranslate"><span class="pre">debug</span></code> and <code class="docutils literal notranslate"><span class="pre">debug(Group)</span></code> messages are only printed
when the <code class="docutils literal notranslate"><span class="pre">debug</span></code> flag is turned on. These messages are also suppressed
when compiling code with the <code class="docutils literal notranslate"><span class="pre">optimize</span></code> flag turned on. This tool
supports selective enabling of <code class="docutils literal notranslate"><span class="pre">debug</span></code> and <code class="docutils literal notranslate"><span class="pre">debug(Group)</span></code> messages
in normal and debug modes.</p>
<section id="api-documentation">
<h2>API documentation<a class="headerlink" href="#api-documentation" title="Link to this heading"></a></h2>
<p>This tool API documentation is available at:</p>
<p><a class="reference external" href="../../apis/library_index.html#debug-messages">../../apis/library_index.html#debug-messages</a></p>
<p>For general information on debugging, open in a web browser the
following link and consult the debugging section of the User Manual:</p>
<p><a class="reference external" href="../../handbook/userman/debugging.html">../../handbook/userman/debugging.html</a></p>
</section>
<section id="loading">
<h2>Loading<a class="headerlink" href="#loading" title="Link to this heading"></a></h2>
<p>This tool can be loaded using the query:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(debug_messages(loader)).
</pre></div>
</div>
</section>
<section id="testing">
<h2>Testing<a class="headerlink" href="#testing" title="Link to this heading"></a></h2>
<p>To test this tool, load the <code class="docutils literal notranslate"><span class="pre">tester.lgt</span></code> file:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">logtalk_load</span>(debug_messages(tester)).
</pre></div>
</div>
</section>
<section id="usage">
<h2>Usage<a class="headerlink" href="#usage" title="Link to this heading"></a></h2>
<p>The tool provides two sets of predicates. The first set allows enabling
and disabling of all <code class="docutils literal notranslate"><span class="pre">debug</span></code> and <code class="docutils literal notranslate"><span class="pre">debug(Group)</span></code> messages for a given
component. The second set allows enabling and disabling of
<code class="docutils literal notranslate"><span class="pre">debug(Group)</span></code> messages for a given group and component for
fine-grained control.</p>
<p>Upon loading the tool, all debug messages are skipped. The user is then
expected to use the tool API to selectively enable the messages that
will be printed. As an example, consider the following object, part of a
<code class="docutils literal notranslate"><span class="pre">xyz</span></code> component:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span><span class="p">:- </span><span class="k">object</span>(foo).

<span class="p">    :- </span><span class="k">public</span>([bar<span class="o">/</span><span class="m">0</span>, baz<span class="o">/</span><span class="m">0</span>]).
<span class="p">    :- </span><span class="k">uses</span>(logtalk, [print_message<span class="o">/</span><span class="m">3</span>]).

    bar <span class="o">:-</span>
        print_message(debug(bar), xyz, <span class="o">@</span><span class="s">&#39;bar/0 called&#39;</span>).

    baz <span class="o">:-</span>
        print_message(debug(baz), xyz, <span class="o">@</span><span class="s">&#39;baz/0 called&#39;</span>).

<span class="p">:- </span><span class="k">end_object</span>.
</pre></div>
</div>
<p>Assuming the object <code class="docutils literal notranslate"><span class="pre">foo</span></code> is compiled and loaded in normal or debug
mode, after also loading this tool, <code class="docutils literal notranslate"><span class="pre">bar/0</span></code> and <code class="docutils literal notranslate"><span class="pre">baz/0</span></code> messages
will not print any debug messages:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> <span class="k">{</span>debug_messages(loader), foo<span class="k">}</span>.
...
yes

| <span class="o">?-</span> foo<span class="o">::</span>(bar, baz).
yes
</pre></div>
</div>
<p>We can then enable all debug messages for the <code class="docutils literal notranslate"><span class="pre">xyz</span></code> component:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> debug_messages<span class="o">::</span>enable(xyx).
yes

| <span class="o">?-</span> foo<span class="o">::</span>(bar, baz).
bar<span class="o">/</span><span class="m">0</span> called
baz<span class="o">/</span><span class="m">0</span> called
yes
</pre></div>
</div>
<p>Or we can selectively enable only debug messages for a specific group:</p>
<div class="highlight-logtalk notranslate"><div class="highlight"><pre><span></span>| <span class="o">?-</span> debug_messages<span class="o">::</span>disable(xyx).
yes

| <span class="o">?-</span> debug_messages<span class="o">::</span>enable(xyx, bar).
yes

| <span class="o">?-</span> foo<span class="o">::</span>(bar, baz).
bar<span class="o">/</span><span class="m">0</span> called
yes
</pre></div>
</div>
</section>
</section>


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